Nitride Semiconductor Light Emitting Device and Fabrication Method Thereof

ABSTRACT

Provided is a nitride semiconductor light emitting device including: a first nitride semiconductor layer; an active layer formed above the first nitride semiconductor layer; and a delta doped second nitride semiconductor layer formed above the active layer. According to the present invention, the optical power of the nitride semiconductor light emitting device is enhanced, optical power down phenomenon is improved and reliability against ESD (electro static discharge) is enhanced.

TECHNICAL FIELD

The present invention is relative to a nitride semiconductor lightemitting device and fabrication method thereof, and to a nitridesemiconductor light emitting device and a fabrication method thereofthat can increase the optical power and enhance the reliability byincreasing a hole carrier concentration contributing to the electricconductivity in an electrode contact layer to increase the recombinationprobability of electrons and holes.

BACKGROUND ART

A schematic stack structure of a general nitride semiconductor lightemitting device and a fabrication method thereof will now be described.

FIG. 1 is a sectional view of a general nitride semiconductor lightemitting device.

Referring to FIG. 1, a conventional nitride semiconductor light emittingdevice includes a substrate 101, a buffer layer 103, an n-GaN layer 105,an active layer 107 and a p-GaN layer 109. Herein, the substrate 101 canbe exemplified by a sapphire substrate.

A fabrication method of the nitride semiconductor light emitting devicewill now be described. In order to minimize the occurrence of crystaldefects due to differences in the lattice constants and the thermalexpansion coefficients of the substrate 101 and the n-GaN layer 105, aGaN-based nitride or an AlN-based nitride having an amorphous phase at alow temperature is formed as the buffer layer 103.

The n-GaN layer 105 doped with silicon at a doping concentration of10¹⁸/□ is formed at a high temperature as a first electrode contactlayer. Thereafter, the growth temperature is lowered and the activelayer 107 is formed. Thereafter, the growth temperature is againelevated and the p-GaN layer 109 doped with magnesium (Mg) and having athickness range of 0.1-0.5 □ is formed as a second electrode contactlayer. The nitride semiconductor light emitting device having theaforementioned stack structure is formed in a p-/n-junction structurewhich uses the n-GaN layer 105 as the first electrode contact layer anduses the p-GaN layer 109 as the second electrode contact layer.

Also, a second electrode material formed on the second electrode contactlayer is limited depending on a doping type of the second electrodecontact layer. For example, in order to decrease the contact resistancebetween the second contact material and the p-GaN layer 109 having ahigh resistance component and enhance the current spreading, a thintransmissive resistance material of a Ni/Au alloy is used as the secondelectrode material.

To form the p-GaN layer 109 used as the second electrode contact layer,the p-/n-junction light emitting device using the nitride semiconductoremploys a doping source of Cp2Mg or DMZn. In the case of DMZn, since Znis in ‘deep energy level’ within the p-GaN layer 109 and has a very highactivation energy, the hole carrier concentration serving as a carrierwhen a bias is applied is limited to about 1×10¹⁷/□. Accordingly, Cp2MgMO (metal organic) having a low activation energy is used as the dopingsource.

Also, when the Mg-doped p-GaN layer 109 having a thickness range of0.1-0.5 □ is grown using a doping source of Cp2Mg at the same flow rateor by sequentially varying the flow rate of Cp2Mg, hydrogen (H) gasseparated from the doping source and NH3 carrier gas are combined toform an Mg—H complex, in the p-GaN layer 109, which shows a highresistance insulation characteristic of more than ˜10⁶Ω. Accordingly, inorder to emit light during the recombination process of holes andelectrons in the active layer 107, an activation process is essentiallyrequired to break the bond of Mg—H complex. Since the Mg-doped p-GaNlayer 109 has a high resistance, it can not be used without any change.The activation process is performed through an annealing process at antemperature range of 600-800° C. in an ambient of N2, N2/O2. However,since Mg existing in the p-GaN layer 109 has a low activationefficiency, it has a relatively high resistance value compared with then-GaN layer 105 used as the first electrode contact layer. In realcircumstance, after the activation process, the atomic concentration ofMg in the p-GaN layer 109 is in a range of 10¹⁹/□-10²⁰/□, and the holecarrier concentration contributing to a pure carrier conductivity is ina range of 10¹⁷/□-10¹⁸/□, which correspond to a difference of maximum10³ times. It is also reported that the hole mobility is 10 □/vsec,which is a very low value. FIG. 2 is a schematic view showing asectional structure of the conventional Mg-doped p-GaN layer and an Mgprofile inside the Mg-doped p-GaN layer after the activation process isperformed. Referring to FIG. 2, it can be seen that the Mg atomicconcentration and the hole carrier concentration show a difference ofmaximum 10³ times.

Meanwhile, the Mg atomic concentration remaining in the p-GaN layer 109without a complete activation causes many problems. For example, lightemitting from the active layer toward the surface is trapped to lowerthe optical power, or when a high current is applied, heat is generateddue to a relatively high resistance value, so that the life time of thelight emitting device is shortened to have a fatal influence on thereliability. Especially, in the case of a large size/high power 1 □×1 □light emitting device using a flip chip technique, since a current of350 mA which is very higher than a conventional current of 20 mA isapplied, a junction temperature of more than 100° C. is generated at ajunction face, having a fatal influence on the device reliability andcausing a limitation to product application in future. The generatedmuch heat is caused by an increase of resistance component due to the Mgatomic concentration remaining in the p-GaN layer 109 used as the secondelectrode contact layer without being activated as a carrier, and arough surface property due to the increase of the resistance component.

Also, in the general p-/n-junction light emitting device, the n-GaNlayer 105 used as the first electrode contact layer can easily controlthe hole concentration within 5-6×10¹⁸/□ within a critical thicknessensuring the crystallinity in proportional to the silicon dopingconcentration depending on an increase in the flow rate of SiH4 orSi2H6, whilst in the p-GaN layer 109 used as the second electrodecontact layer, the hole concentration substantially serving as carriersis limited within a range of 1-9×10¹⁷/□ although the flow rate of Cp2Mgis increased and Mg atoms of more than maximum ˜10²⁰/□ are doped. Tothis end, the conventional light emitting device is made in ap-/n-junction structure having an asymmetric doping profile.

As aforementioned, the low carrier concentration and high resistancecomponent of the p-GaN layer 109 used as the second electrode contactlayer cause the light emitting efficiency to be decreased.

To solve the above problem, a conventional method for increasing theoptical power by employing Ni/Au TM (transparent thin metal) having agood transmission and a low contact resistance has been proposed.However, the conventional method badly influences the device reliabilitywhen being applied to a large size/high power light emitting device.This problem still remains unsettled in the light emitting devices usingthe GaN semiconductor.

DISCLOSURE OF INVENTION Technical Problem

The present invention provides a nitride semiconductor light emittingdevice and fabrication method thereof that can enhance the property ofp-GaN layer constituting the nitride semiconductor light emittingdevice.

Also, the present invention provides a nitride semiconductor lightemitting device and fabrication method thereof that can enhance theoptical power and reliability.

In addition, the present invention provides a nitride semiconductorlight emitting device and fabrication method thereof that can overcomethe problems caused by the low hole carrier concentration and mobilityof the Mg-doped p-GaN layer used as the second electrode contact layerand a high resistance component of Mg atomic concentration (includingMg—H complex) remaining completely inactivated in the p-GaN layer, andenhance the optical power and reliability.

Technical Solution

There is provided a nitride semiconductor light emitting deviceincluding: a first nitride semiconductor layer; an active layer formedabove the first nitride semiconductor layer; and a delta doped secondnitride semiconductor layer formed above the active layer.

In another aspect of the present invention, there is provided a nitridesemiconductor light emitting device including: a buffer layer; a firstnitride semiconductor layer formed above the buffer layer; a firstelectrode contact layer formed above the first nitride semiconductorlayer; an active layer formed above the first nitride semiconductorlayer in a single quantum well structure or a multi quantum wellstructure comprised of a well layer and a barrier layer; and a deltadoped second nitride semiconductor layer formed above the active layer.

In another aspect of the present invention, there is provided a methodof fabricating a nitride semiconductor light emitting device, the methodincluding: forming a buffer layer above a substrate; forming a firstnitride semiconductor layer above the buffer layer; forming an activelayer above the first nitride semiconductor layer; and forming a deltadoped second nitride semiconductor layer above the active layer.

ADVANTAGEOUS EFFECTS

According to the present invention, the characteristic of the p-GaNlayer constituting the nitride semiconductor light emitting device isenhanced, the optical power of the nitride semiconductor light emittingdevice is enhanced, the optical power down phenomenon is improved, andthe reliability against ESD (Electro Static Discharge) is enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The spirit of the present invention will be understood more apparentlyfrom the accompanying drawings. In the drawings:

FIG. 1 is a schematic view showing a stack structure of a generalnitride semiconductor light emitting device;

FIG. 2 is a schematic view showing a sectional structure of theconventional Mg-doped p-GaN layer and an Mg profile inside the Mg-dopedp-GaN layer after the activation process is performed;

FIG. 3 is a schematic view illustrating a Cp2Mg delta doping flow rateaccording to a growth time;

FIG. 4 is a graph showing an Mg doping profile before and after asubsequent activation process after a crystal growth for a Cp2Mg deltadoped p-GaN is completed;

FIG. 5 is a graph showing an electric field profile after a subsequentactivation process of a Cp2Mg delta doped p-GaN layer is completed;

FIG. 6 is a schematic view showing a stack structure of a nitridesemiconductor light emitting device according to a first embodiment ofthe present invention; and

FIG. 7 is a schematic view showing a stack structure of a nitridesemiconductor light emitting device according to a second embodiment ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment according to the spirit of the presentinvention will be described with reference to the accompanying drawings.

The present invention is characterized in that in the fabrication methodof a nitride semiconductor, a Cp2Mg delta doping process is performed togrow a p-GaN layer, and the Cp2Mg delta doping process will be describedwith reference to FIGS. 3 to 5.

FIG. 3 is a schematic view illustrating a Cp2Mg delta doping flow rateaccording to a growth time.

Referring to FIG. 3, after an active layer emitting light is grown, anundoped GaN layer of less than 200 Å is grown so as to protect a “V” pitdefect formed during the growth of the active layer, and the flow rateof Cp2Mg is adjusted from 0 cc to 1000 cc within a thickness range of10-200 Å to form a delta doped GaN layer. FIG. 3 shows an Mg-delta dopedGaN grown by consecutively repeating one period consisting of undopedGaN layer/delta doped GaN layer. In the above crystal growth method,only the flow rate of Cp2Mg is changed, the growth temperature is fixedto 1000° C. and the other conditions are fixed so as to maintain thecrystallinity.

In growing the Mg-delta doped GaN layer, the thickness of each of theundoped GaN layer and the delta doped GaN layer constituting one periodmay be varied. Also, In repeatedly growing one period of undoped GaNlayer/delta doped GaN layer, the dose at each period may be varied. Atthis time, an overall thickness of the two layers forming one period canbe adjusted within a thickness range of 10-300 Å.

FIG. 4 is a graph showing an Mg doping profile before and after asubsequent activation process after a crystal growth for a Cp2Mg deltadoped p-GaN is completed.

Referring to FIG. 4, when Cp2Mg delta doping of the same amount isrepeated at a constant period before the subsequent activation process,the delta doped GaN layer having a sharp Mg doping profile can beobtained at a boundary between the undoped GaN layers. Thereafter, whilethe subsequent activation process is performed, Mg is diffused into theundoped GaN layers of both sides, so that a wide Mg doping profile isobtained. Through the above subsequent activation process, the p-GaNlayer has a uniform Mg doping profile in whole.

In general, when a forward bias is applied to the undoped GaN layer, itcan be seen that the operating voltage increases. In the presentinvention, the operating voltage can be effectively lowered to less than3.5 V (20 mA) to increase the optical power of the light emitting deviceby controlling the thickness of the Cp2Mg delta doped p-GaN layer andthe thickness of the undoped GaN layer.

FIG. 5 is a graph showing an electric field profile after a subsequentactivation process of a Cp2Mg delta doped p-GaN layer is completed.

Referring to FIG. 5, it can be seen that the hole carrier concentrationprofile is relatively high in the Cp2Mg delta doped regions periodicallyrepeated. Therefore, in the Cp2Mg delta doped regions, potentialincreases to form an electric field doping. Accordingly, like in an HEMTstructure 2 DEG (two dimensional electronic well layer) that is a highspeed switching device using an energy bandgap difference (AlGaN/GaNjunction), potential well can be formed to uniformly and effectivelycontrol the flow of holes likewise to effectively control atwo-dimensional flow of electrons. In conclusion, it can be seen thathole injection efficiency is increased by the potential well.

As can be seen from the above description, the p-GaN layer grown by thec onventional art has a problem that when a forward bias is applied, ahigh resistance component thereof sharply decreases current flow ininverse proportion with a distance from an electrode contact surface toan upper surface thereof, whilst in the present invention, the potentialwell layer can more effectively increase the current density to enhancethe optical power of the light emitting device.

Also, by the Cp2Mg delta doping, since the doping element is uniformly,repeatedly and periodically doped at a relatively very small amount andthen the activation process for the p-GaN layer is optimized andperformed, the atomic concentration of Mg, Mg—H complex and the likeexisting therein can be decreased to suppress the resistance componentas much as possible. In other words, the present invention increases thehole carrier concentration purely contributing to the electricconductivity to thereby increase the recombination probability withelectrons and in the long run effectively increase the optical power.Thus, the present invention provides a high level crystal growthtechnique that can decrease the resistance component to enhance thereliability of the light emitting device.

Hereinafter, a concrete embodiment of the nitride semiconductor lightemitting device according to the present invention will be described.

FIG. 6 is a schematic view showing a stack structure of a nitridesemiconductor light emitting device according to a first embodiment ofthe present invention.

Referring to FIG. 6, the nitride semiconductor light emitting deviceaccording to the present embodiment includes a substrate 401, a bufferlayer 403, an In-doped GaN layer 405, an n-GaN layer 407, a low-moleIn-doped GaN layer or low-mole InGaN layer 409, an active layer 411, andan Mg-delta doped p-GaN layer 413. The Mg-delta doped p-GaN layer 413has been described in detail with reference to FIGS. 3 to 5.

Hereinafter, a fabrication method of the nitride semiconductor lightemitting device according to a first embodiment will be described inmore detail.

First, in the present embodiment, only H2 carrier gas is supplied ontothe sapphire substrate 401 at a high temperature to clean the sapphiresubstrate 401. Thereafter, in step of decreasing the growth temperatureto 540° C., NH3 source gas is supplied to perform a nitridation of thesapphire substrate 401, for example for 7 minutes.

Thereafter, the buffer layer 403 having a 1^(st) AlInN/1^(st) GaN/2^(nd)AlInN/2^(nd) GaN structure is grown to a thickness of about 500 Å.Herein, the buffer layer 403 can be formed in a structure selected fromthe group consisting of a stack structure of AlInN/GaN, a super latticestructure of InGaN/GaN, a stack structure of InXGa1−XN/GaN, and a stackstructure of AlXInYGa1−(X+Y)N/InXGa1−XN/GaN. Then, the growthtemperature is increased up to 1060° C. for 6 minutes, the lowtemperature buffer layer 403 is recrystallized in a mixture ambient ofNH3 source gas and H2 carrier gas for 2 minutes, and at the same growthtemperature, the indium-doped GaN layer 405 having about 2 □ thicknessis grown in a single crystal.

Thereafter, the growth temperature is decreased to 1050° C., and then-GaN layer 407 co-doped with silicon and indium at the same growthtemperature is grown to a thickness of 2 □. The n-GaN layer 407 is usedas the first electrode layer.

Also, to adjust the strain of the active layer 411, the low-moleIn-doped GaN layer or low-mole InGaN layer 409 having 5% indium content(wavelength: 480 nm) is grown to a thickness of 300 Å at 750° C. Theindium content can be adjusted in a range of 1-5%. The low-mole In-dopedGaN layer or low-mole InGaN layer 409 is intentionally controlled in‘spiral growth mode’ having a uniform profile. Herein, in the low-moleIn-doped GaN layer or low-mole InGaN layer 409, as the ‘spiral density’intentionally controlled increases, the area of the active layer 411increases. Accordingly, the low-mole In-doped GaN layer or low-moleInGaN layer 409 can perform a role that can increase the light emittingefficiency.

Thereafter, at the same growth temperature, the active layer 411 havinga single quantum well (SQW) of undoped InGaN/InGaN structure is grown.In the grown active layer 411, the barrier layer has an indium contentof less than 5% and a thickness of about 250 Å. At this time, the activelayer 411 can be formed in the multi quantum well layer.

Thereafter, the growth temperature is again increased to 1000° C., anoverall thickness is fixed to 0.1 □, the flow rate of TMGa is alsofixed, and only the flow rate of Cp2Mg is switched on/off from 0 cc to1000 cc to thereby perform the delta doping process. In order toeffectively perform the Cp2Mg delta doping, after the active layer 411emitting light is grown, the undoped GaN layer is first grown in athickness range of 10-200 Å to completely protect the active layer 411such that Mg atoms is not internally diffused into the “V” pit crystalformed on a surface of the active layer 411, and then the Cp2Mg deltadoping process is performed in a thickness range of 10-200 Å. The Cp2Mgdelta doping process sets the undoped GaN/delta doped GaN structure asone period and continuously repeats the one period within an overallthickness of 0.1 □ to form a light emitting device having ap-/n-junction structure such that resistance component is decreased byMg atomic concentration (including Mg atomic and Mg—H complex) after theactivation and uniform carrier concentration is obtained.

After the nitride semiconductor light emitting device is completed bythe aforementioned processes, mesa etching is performed using an ICPetching apparatus and the nitride semiconductor light emitting device ismade in a size of 330 □×205 □. Electrical property variation of thefabricated nitride semiconductor light emitting device is analyzed andinvestigated to verify its performance. As a result, the operatingvoltage (20 mA) in a forward bias is below 3.4 V, which is the samevalue as that of the conventional art, but the optical power isincreased by 50-100%.

Why the optical power is increased is that an inner diffusion into the“V” pit defect formed in the surface of the active layer emitting lightis suppressed, and an absolute amount of Mg atomic (including Mg—Hcomplex) remaining in the layer after the subsequent activation processis decreased by an Mg doping profile lower than that of the conventionalart, but the hole carrier concentration contributing to the electricconductivity is increased.

FIG. 7 shows a nitride semiconductor light emitting device according toa second embodiment of the present invention.

Referring to FIG. 7, the nitride semiconductor light emitting deviceaccording to a second embodiment of the present invention includes asubstrate 401, a buffer layer 403, an In-doped GaN layer 405, an n-GaNlayer 407, a low-mole In-doped GaN layer or low-mole InGaN layer 409, anactive layer 411, an Mg-delta doped p-GaN layer 413, and an n-InGaNlayer 515.

Compared with the first embodiment, the above second embodiment has adifference in that the nitride semiconductor light emitting devicefurther includes the n-InGaN layer 515. Therefore, only the n-InGaNlayer 515 will be additively described and descriptions of otherelements will be referred from that of the first embodiment.

To fabricate an n-/p-/n-junction structure light emitting device, inaddition to the p-/n-junction structure light emitting device, thesecond embodiment of the present invention grows the Mg-delta dopedp-GaN layer 413 and then grows the n-InGaN layer 515 to use as thesecond electrode contact layer.

The n-InGaN layer 515 used as the second electrode contact layer isgrown to a thickness of 50 Å with being doped with silicon at a growthtemperature decreased to 800° C. in a mixture gas ambient of NH3 sourcegas and N2 carrier gas. At this time, the n-InGaN layer 515 is used asthe second electrode contact layer and is designed to have the supergrading (SG) structure in which indium content is adjusted to controlthe energy bandgap profile on whole. By the aforementioned method, then-/p-/n-junction structure nitride semiconductor light emitting devicecan be obtained.

MODE FOR THE INVENTION

In addition to the above embodiments, a plurality of other examples canbe provided on the basis of the same spirit.

First, a transparent electrode may be further formed on the n-InGaNlayer 515. The transparent electrode can be formed of one selected fromthe group consisting of ITO, IZO(In—ZnO), GZO(Ga—ZnO), AZO(Al—ZnO),AGZO(Al—Ga ZnO), IGZO(In—Ga ZnO), IrOX, RuOX, RuOX/ITO, Ni/IrOX/Au, andNi/IrOX/Au/ITO.

Also, while the second embodiment illustrates that the n-InGaN layer 515is formed as the second electrode contact layer, an n-InGaN/InGaN superlattice structure may be formed as the second electrode contact layer.Alternatively, a Si-doped GaN layer may be further formed between then-InGaN/InGaN super lattice layer and the Mg-delta doped p-GaN layer413.

In addition, the first and second embodiments illustrate that Mg isdelta doped in the delta doping process. However, through a similarprocess, Mg—Al, Mg—Al—In or the like as well as Mg can be delta doped.At this time, TMAl, TMIn MO (metal organic) can be used as a dopingsource.

Further, the delta doped p-GaN layer can be formed with one periodconsisting of undoped AlGaN/delta doped p-GaN structure, the two layersconstituting the one period can repeatedly grown at least two times, theundoped AlGaN layer is grown within a thickness range of 10-300 Å withan Al composition range of 0.01-0.02.

Furthermore, the delta doped p-GaN layer can be formed with one periodconsisting of undoped InGaN/delta doped p-GaN structure, the two layersconstituting the one period can repeatedly grown at least two times, theundoped InGaN layer is grown within a thickness range of 10-300 Å withan Al composition range of 0.01-0.1.

Also, the delta doped p-GaN layer can be formed with one periodconsisting of undoped GaN/undoped AlGaN cap/delta doped p-GaN structure,the three layers constituting the one period can repeatedly grown atleast two times, the undoped AlGaN cap layer is grown within a thicknessrange of 5-200 Å with an Al composition range of 0.01-0.02.

Additionally, the delta doped p-GaN layer can be formed with one periodconsisting of undoped InGaN/undoped AlGaN cap/delta doped p-GaNstructure, the three layers constituting the one period can repeatedlygrown at least two times, the undoped AlGaN cap layer is grown within athickness range of 5-200 Å with an Al composition range of 0.01-0.02.

Also, in the first and second embodiments, the n-GaN layer serving asthe first electrode contact layer can be an n-GaN layer formed by aco-doping of Si and In, and it can be formed at a doping concentrationof 1-9×10¹⁹/cm³ in a thickness range of 1-4 □.

Additionally, the first electrode contact layer can be formed with oneperiod consisting of undoped-AlGaN/doped-GaN super lattice structure,the two layers constituting the one period can be repeatedly grown atleast two times with an overall thickness of 1-2 □ and an Al compositionof 0.05-0.3. The doped-GaN layer can be formed within a thickness rangeof 200-500 Å.

Further, the active layer can be made in a single quantum well structureor a multi quantum well structure comprised of well layer/SiNx clusterlayer/barrier layer, and the SiNx cluster layer can be grown by aSi-delta doping method. The SiNx cluster layer can be grown by theSi-delta doping using a doping source of SiH4 or SiH6 alone.

INDUSTRIAL APPLICABILITY

According to the nitride semiconductor light emitting device andfabrication method thereof provided by the present invention, theoptical power is enhanced, the power down phenomenon is improved, andthe reliability against ESD (Electro Static Discharge) is enhanced.

Also, the present invention can be applied to a lighting apparatusrequiring high optical power and high reliability.

1. A nitride semiconductor light emitting device comprising: a firstnitride semiconductor layer; an active layer formed above the firstnitride semiconductor layer; and a delta doped second nitridesemiconductor layer formed above the active layer.
 2. The nitridesemiconductor light emitting device according to claim 1, furthercomprising a third nitride semiconductor layer formed above the deltadoped second nitride semiconductor layer.
 3. The nitride semiconductorlight emitting device according to claim 2, wherein the third nitridesemiconductor layer is formed of an n-InGaN layer with an SG (supergrading) structure in which indium content is gradually varied, or of ann-InGaN/InGaN super lattice structure layer.
 4. The nitridesemiconductor light emitting device according to claim 2, furthercomprising a Si-doped GaN layer formed between the third nitridesemiconductor layer and the delta doped second nitride semiconductorlayer.
 5. The nitride semiconductor light emitting device according toclaim 2, further comprising a transparent electrode formed above thethird nitride semiconductor layer.
 6. The nitride semiconductor lightemitting device according to claim 5, wherein the transparent electrodeis formed of one selected from the group consisting of ITO, IZO(In—ZnO),GZO(Ga—ZnO), AZO(Al—ZnO), AGZO(Al—Ga ZnO), IGZO(In—Ga ZnO), IrO_(x),RuO_(x), RuO_(x)/ITO, Ni/IrO_(x)/Au, and Ni/IrO_(x)/Au/ITO.
 7. Thenitride semiconductor light emitting device according to claim 1,further comprising: a buffer layer disposed below the first nitridesemiconductor layer; and a substrate disposed below the buffer layer. 8.The nitride semiconductor light emitting device according to claim 7,further comprising a strain control layer disposed above the bufferlayer.
 9. The nitride semiconductor light emitting device according toclaim 7, wherein the buffer layer has a structure selected from thegroup consisting of a stack structure of AlInN/GaN, a super latticestructure of InGaN/GaN, a stack structure of In_(x)Ga_(1−x)N/GaN, and astack structure of Al_(x)In_(y)Ga_(1−(x+y))N/In_(x)Ga_(1−x)N/GaN. 10.The nitride semiconductor light emitting device according to claim 1,further comprising a low mole indium-containing nitride layer formedbetween the first nitride semiconductor layer and the active layer,wherein the low mole indium-containing nitride layer has an indiumcontent of 1-5%.
 11. The nitride semiconductor light emitting deviceaccording to claim 1, wherein the delta doped second nitridesemiconductor layer is grown in a thickness range of 10-300 Å.
 12. Thenitride semiconductor light emitting device according to claim 1,wherein the delta doped second nitride semiconductor layer is arepeatedly grown structure selected from the group consisting of undopedGaN/delta doped p-GaN, undoped AlGaN/delta doped p-GaN, undopedInGaN/delta doped p-GaN, undoped GaN/undoped AlGaN cap/delta dopedp-GaN, and undoped InGaN/undoped AlGaN cap/delta doped p-GaN structures.13. The nitride semiconductor light emitting device according to claim1, wherein the delta doped second nitride semiconductor layer is formedwith at least one period consisting of layers where the doping dose ischanged, wherein the period is repeatedly grown in the delta dopedsecond nitride semiconductor layer.
 14. The nitride semiconductor lightemitting device according to claim 1, wherein the delta doped secondnitride semiconductor layer comprises one selected from the groupconsisting of Mg delta doped GaN layer, Mg—Al delta doped GaN layer andMg—Al—In delta doped GaN layer.
 15. The nitride semiconductor lightemitting device according to claim 1, wherein the delta doped secondnitride semiconductor layer is grown repeatedly at least two times whereone period is one selected from the group consisting of undoped GaNlayer/delta doped p-GaN layer, undoped AlGaN layer/delta doped p-GaNlayer, undoped InGaN layer/delta doped p-GaN layer, undoped GaNlayer/undoped AlGaN cap layer/delta doped p-GaN layer, and undoped InGaNlayer/undoped AlGaN cap layer/delta doped p-GaN layer structures suchthat the selected layers constituting the one period have differentthicknesses.
 16. The nitride semiconductor light emitting deviceaccording to claim 15, wherein the undoped AlGaN layer is grown in athickness range of 10-300 Å with an Al composition of 1-2%.
 17. Thenitride semiconductor light emitting device according to claim 15,wherein the undoped InGaN layer is grown in a thickness range of 10-300Å with an In composition of 1-2%.
 18. The nitride semiconductor lightemitting device according to claim 15, wherein the undoped AlGaN caplayer is grown in a thickness range of 5-200 Å with an Al composition of1-2%.
 19. The nitride semiconductor light emitting device according toclaim 1, wherein the first nitride semiconductor layer is an n-GaN layerformed by a Si—In simultaneous doping in a doping concentration range of1×10¹⁹/cm³−9×10¹⁹/cm³ at a thickness range of 1-4 μm.
 20. The nitridesemiconductor light emitting device according to claim 1, wherein thefirst nitride semiconductor layer is formed in an overall thickness lessthan 2 μm by growing repeatedly at least two times anundoped-AlGaN/doped-GaN super lattice structure.
 21. The nitridesemiconductor light emitting device according to claim 20, wherein theundoped-AlGaN layer is formed in a thickness range of 10-200 Å with anAl composition of 0.05-0.3, and the doped-GaN layer is formed in athickness range of 200-500 Å.
 22. A nitride semiconductor light emittingdevice comprising: a buffer layer; a first nitride semiconductor layerformed above the buffer layer; a first electrode contact layer formedabove the first nitride semiconductor layer; an active layer formedabove the first nitride semiconductor layer in a single quantum wellstructure or a multi quantum well structure comprising a well layer anda barrier layer; and an Mg-delta doped second nitride semiconductorlayer formed above the active layer.
 23. The nitride semiconductor lightemitting device according to claim 22, wherein the Mg-delta doped secondnitride semiconductor layer is a second electrode contact layer.
 24. Thenitride semiconductor light emitting device according to claim 22,further comprising an n-type second electrode contact layer formed abovethe Mg-delta doped second nitride semiconductor layer.
 25. The nitridesemiconductor light emitting device according to claim 22, wherein theactive layer further comprises an SiNx cluster layer interposed betweenthe well layer and the barrier layer.
 26. The nitride semiconductorlight emitting device according to claim 25, wherein the SiNx clusterlayer is grown using a Si-delta doping method.
 27. A method offabricating a nitride semiconductor light emitting device, the methodcomprising: forming a buffer layer above a substrate; forming a firstnitride semiconductor layer above the buffer layer; forming an activelayer above the first nitride semiconductor layer; and forming a deltadoped second nitride semiconductor layer above the active layer.
 28. Themethod according to claim 27, wherein the buffer layer has a structureselected from the group consisting of a stack structure of AlInN/GaN, asuper lattice structure of InGaN/GaN, a stack structure ofIn_(x)Ga_(1−x)N/GaN and a stack structure ofAl_(x)In_(y)Ga_(1−x(x+y))N/In_(x)Ga_(1−x)N/GaN.
 29. The method accordingto claim 27, prior to forming the active layer, further comprisingforming a low mole nitride semiconductor layer having an indium contentof 1-5%.
 30. The method according to claim 27, wherein the delta dopedsecond nitride semiconductor layer comprises one selected from the groupconsisting of Mg delta doped GaN layer, Mg—Al delta doped GaN layer andMg—Al—In delta doped GaN layer.
 31. The method according to claim 27,wherein the delta doped second nitride semiconductor layer is grown in athickness range of 10-300 Å using Cp2Mg or DMZn MO (metal organic)source.
 32. The method according to claim 27, wherein forming the deltadoped second nitride semiconductor layer comprises growing repeatedly atleast one time a structure selected from the group consisting of undopedGaN layer/delta doped p-GaN layer, undoped AlGaN layer/delta doped p-GaNlayer, undoped InGaN layer/delta doped p-GaN layer, undoped GaNlayer/undoped AlGaN cap layer/delta doped p-GaN layer and undoped InGaNlayer/undoped AlGaN cap layer/delta doped p-GaN layer structures. 33.The method according to claim 27, wherein the delta doped second nitridesemiconductor layer is formed with at least one period consisting oflayers where the doping dose is changed, wherein the period isrepeatedly grown in the delta doped second nitride semiconductor layer.34. The method according to claim 27, wherein the delta doped secondnitride semiconductor layer has a doping source of any of Cp₂Mg and DMZnMO, or of any of TMAl and TMIn MO together with any of Cp₂Mg and DMZnMO.
 35. The method according to claim 27, wherein forming the deltadoped second nitride semiconductor layer comprises growing structuresrepeatedly at least two times, wherein one period of growth is astructure selected from the group consisting of undoped GaN layer/deltadoped p-GaN layer, undoped AlGaN layer/delta doped p-GaN layer, undopedInGaN layer/delta doped p-GaN layer, undoped GaN layer/undoped AlGaN caplayer/delta doped p-GaN layer, and undoped InGaN layer/undoped AlGaN caplayer/delta doped p-GaN layer structures, wherein the selected layersconstituting the one period have different thicknesses.
 36. The methodaccording to claim 35, wherein the undoped AlGaN layer is grown in athickness range of 10-300 Å with an Al composition of 1-2%.
 37. Themethod according to claim 35, wherein the undoped InGaN layer is grownin a thickness range of 10-300 Å with an In composition of 1-2%.
 38. Themethod according to claim 35, wherein the undoped AlGaN cap layer isgrown in a thickness range of 5-200 Å with an Al composition of 1-2%.39. The method according to claim 27, further comprising forming a thirdnitride semiconductor layer above the delta doped second nitridesemiconductor layer.
 40. The method according to claim 39, wherein thethird nitride semiconductor layer is formed of an n-InGaN layer with anSG (super grading) structure in which indium content is graduallyvaried, or of an n-InGaN/InGaN super lattice structure layer.
 41. Themethod according to claim 39, further comprising forming a Si-doped GaNlayer between the third nitride semiconductor layer and the delta dopedsecond nitride semiconductor layer.
 42. The method according to claim27, further comprising forming an indium-doped nitride semiconductorlayer after forming the buffer layer.
 43. The method according to claim27, wherein the active layer is provided in a single quantum wellstructure or a multi quantum well structure, the active layer comprisinga well layer/SiNx cluster layer/barrier layer.
 44. The method accordingto claim 43, wherein the SiNx cluster layer is grown by a Si-deltadoping using SiH₄ or SiH₆ as a doping source.